Computer networks have
huge numbers of hardware and software components. To troubleshoot Windows networks,
you first must look at the big picture.

Determine the Scope of the Problem

You need to initially take a holistic view and identify the scope
of the problem. Is the problem on all computers, one computer, or a group of
computers with some common characteristic? Is the common characteristic a
switch, a hub, or a server that they access? Once the major area is identified,
you can continue to focus in on the detail that is the cause of the problem.

OR

Check
the Obvious

Initially,
it is important to not overlook obvious mistakes. Do all devices have
power? Are all of the network cables plugged in? Have all error messages and
error logs been viewed and noted? Checking the obvious takes little time and can
avoid unnecessary investigations.

Divide and Conquer

If you do not attack your problems with a systematic
methodology, you will quickly get overwhelmed by the numerous possible
causes of the problem. The strategy that you must adopt is a divide and conquer
approach. Devise a series of tests that will divide the numerous components into
two groups where you know that the problem is in one group and the other group
is problem free. Repeat this approach on the group of components with the
problem until you identify the individual component with the problem.

This methodology can be applied to all sorts of
troubleshooting, but computer networks are unique in that they are composed of
huge numbers of hardware and software components. Computer network
troubleshooting uniquely has different types of fault isolation.

First determine which node in your network
has the problem. I call this first step node isolation.

Second determine if more than one protocol
stack has the problem. If you use both TCP/IP and NWLink/IPX, determin if the problem
is
with Internet access, Netware server access, or both. I call this second step
stack
isolation.

Once you have identified the protocol stack
with the problem, you must determine which layer has the problem. Is the
problem in the network card, IP, TCP, or higher level service. I call this
last step layer isolation.

Use an appropriate tool, to perform your fault
isolation.

Problem Isolation

Type

Example of test

ç?è

Node Isolation

TraceRt shows you the path
through an internet and stops at the node with the problem.

TCP/IP or IPX/SPX

Stack Isolation

Test each protocol stack by
trying an application that uses that protocol.

HTTP

TCP

IP

NDIS

Layer Isolation

A failed PING test tells you
that the
problem is in the Network layer or lower. A successful PING indicates that
the problem is in the Transport layer or above.

Types of Fault Isolation

Layer

Stack

Isolation

Isolation

çNode
Isolationè

TCP/IP

SPX/IPX

LAN

Art
or Science

Computers networks are engineered systems that
can be analyzed and fixed using systematic scientific methodologies. Because of
their dynamic changes and complexity, you can save significant time and effort
by utilizing your intuition and unique knowledge of your environment.

Troubleshooting Steps

Troubleshooting any problem leads to the steps
in the common sense flowchart on the first page. The challenge is to conceive of a
hypothesis and test that will further isolate the source of the problem. For
example, if your web browser will not communicate with a web server, try to
communicate with the PING command to determine if the problem is

an IP communications problem or

a higher level TCP or HTTP web problem.

Try to investigate problems in a test
environment rather than your production network to avoid user interruptions.

Long-Term Goals

Continuously strive to learn about Windows,
network components, protocols, computer hardware, etc. The more you know, the
better you will be at troubleshooting. Read the manuals. Learn about the
troubleshooting tools presented here and develop your own methodology
and toolkit.

These icons represent utilities that are
described in the Tools Section